The present invention relates to circuitry for detecting a current threshold level, and more particularly, to a circuit wherein a very large output current threshold is detected with respect to a low current reference signal.
There are many applications which utilize a current threshold detector circuit. For example, a current detection circuit may be utilized as a current regulator to provide an output current the magnitude of which is maintained at a predetermined level. Thus, if the output current should vary, it is sensed or detected by the current threshold detector to provide a feedback signal to increase or decrease the output current accordingly.
There are other prior art systems in which the safe operation thereof can be exceeded if the level of operating current exceeds a certain threshold level. For instance, DC motor controlled circuits are used in many applications for providing predescribed operations such as automatic window control for automobiles among other things. It is possible that the load current supplied to the motor could, under extreme conditions, exceed the ratings of the motor. If this were to happen, the motor could be damaged or even destroyed. To prevent the foregoing from occurring, prior art systems have required detection means whereby the level of the load current is detected. If the current level exceeds a predetermined threshold level an error output signal is produced which may set a latch circuit to shutdown the motor until such time that the load current therethrough becomes less than the threshold level.
Typically, prior art detection schemes require the use of a sense resistor in the high load current path (through the motor for instance). The load current produces a voltage to be developed across a sense resistor which is monitored by an operational amplifier. The output of the operational amplifier is caused to be switched as the level of the current causes the input of the operational amplifier to switch which activates a latch circuit to shut off the load until such time that the load current is reduced to below the predetermined threshold level.
A serious disadvantage of such prior art detection schemes is that the sense resistor is placed in the high load current path which causes excessive power to be dissipated in the resistor. If the sense resistor is fabricated as a part of an integrated detector circuit, this power dissipation provides undesirable heating of the integrated circuit chip. Moreover, any power dissipated in the sense resistor reduces the available power to the load which also may be undesirable.
Hence, there exists a need for a current threshold detector circuit which overcomes the disadvantage of the prior art schemes as described above.